Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user()

From: Linus Torvalds
Date: Tue Oct 08 2019 - 00:24:47 EST

On Mon, Oct 7, 2019 at 9:09 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> Try the attached patch, and then count the number of "rorx"
> instructions in the kernel. Hint: not many. On my personal config,
> this triggers 15 times in the whole kernel build (not counting
> modules).

.. and four of them are in perf_callchain_user(), and are due to those
"__copy_from_user_nmi()" with either 4-byte or 8-byte copies.

It might as well just use __get_user() instead.

The point being that the silly code in the header files is just
pointless. We shouldn't do it.